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Poof! You're on Earth
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(03-31-2018, 12:40 PM)Cray Wrote: Can you find latitude and longitude of your location on Earth without access to surface landmarks or local clocks?

The sci-fi (or sci-fantasy) situation for this question is:

A group of people have a headquarters on an alternate history Earth, accessible via appropriate gateway device. This alternate history Earth has no humans or civilization other than this HQ building, which is sitting on an anonymous patch of desert that could be anywhere from Australia to the US West. The people running the HQ aren't telling their guests where it's located on alternate Earth. 

The gateway device reaches across time in other ways; the alternate Earth might be thousands of years in a (parallel) future or parallel past. Continents are the same shape, but there could be differences in biomes. The stars may be a bit off.

Guests lack transport to travel far enough to find useful landmarks, but are welcome to bring all sorts of binoculars, portable telescopes, sextants, compasses, reference books/computers, etc.

So, for reasonably educated and equipped people, can they figure out roughly their latitude and longitude? If so, how?

It looks like you could find the latitude with the midday sun. Longitude is harder with no calibrated reference points, correct?

Interesting. Without being able to travel significantly, longitude is basically impossible; one has to have a (completely arbitrary) zero reference point and you just plain don't know where you are in relation to Greenwich. If you have a decently accurate clock you can set wherever you are as zero longitude for use from then on. There are methods for longitude involving moonrise and moonset times that are rather obscure; unless you have a professional astronomer in the party, you probably aren't going to be able to use them.

For latitude, the simplest solution is to wait for nightfall when the sky is clear. Even if the pole star is not the same as it is now (by no means impossible - our north pole star will be different in a time of the order of 10k years) you can find a centre of rotation of the sky. Find its altitude and you're done. With a bit of luck, there will be a star reasonably close to it. (Not the case in the southern hemisphere, in the current epoch.) The problem of whether you are north or south of the equator is also quite simple; when facing the pole, the sky turns in the opposite direction in the southern hemisphere from the north.

Even easier, there are several objects visible in the southern hemisphere that are extremely obvious. The main two are the Magellanic Clouds, and for a period of time probably well in excess of a million years they are going to be there.

BTW. over a period of perhaps 100,000 years a compass is actually unreliable; the period of pole reversals is anywhere from .1 to 1 million years. If you're unlucky, there could be no magnetic field at all. In fact, it's thought that we are just at the start of a pole reversal.

To sum up, given the desert location (thus clear skies most of the time) latitude is reasonably easy, but longitude is impossible. Mostly because it's completely arbitrary in the first place.

One more thing: Unless you are a very long way away in time, local wildlife probably gives you a clue as to roughly where you are; which continent, at least. Kangaroos put you in Australia, for example. And the soil colour is different in Australia and South Africa from SW America or the Sahara. (Or even the Gobi Desert.)

And another; a barometer is going to give you a clue. Much of SW North America is a mile up, as is a significant part of South Africa. High enough up, in fact, that the altitude causes a few problems with cooking. Australia is much lower.
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Messages In This Thread
Poof! You're on Earth - by Cray - 03-31-2018, 12:40 PM
RE: Poof! You're on Earth - by stevebowers - 03-31-2018, 05:16 PM
RE: Poof! You're on Earth - by selden - 03-31-2018, 11:27 PM
RE: Poof! You're on Earth - by JohnnyYesterday - 04-01-2018, 07:46 AM
RE: Poof! You're on Earth - by stevebowers - 04-01-2018, 03:52 PM
RE: Poof! You're on Earth - by Cray - 04-02-2018, 09:32 PM
RE: Poof! You're on Earth - by iancampbell - 04-03-2018, 10:20 AM
RE: Poof! You're on Earth - by Alphadon - 05-03-2018, 05:31 PM
RE: Poof! You're on Earth - by Rynn - 05-03-2018, 07:26 PM
RE: Poof! You're on Earth - by iancampbell - 05-04-2018, 06:49 PM
RE: Poof! You're on Earth - by Rynn - 05-04-2018, 11:43 PM
RE: Poof! You're on Earth - by iancampbell - 05-09-2018, 06:13 PM

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